This invention relates to a high-frequency heating apparatus of a vertical type having a control portion provided below a front door, and more particularly to a microwave oven having an improved cooling mechanism provided in a machine chamber located rearwardly of the control portion.
Heretofore, microwave ovens of a vertical type having a control portion provided upwardly or downwardly of the oven door provided at the front portion of the microwave oven have been widely known. In this type microwave oven, a machine chamber is provided upwardly or downwardly of a heating chamber provided in the microwave oven, and a high-frequency oscillator such as a magnetron and a high-voltage transformer are encased in the machine chamber together with other electrical parts. A cooling fan is also provided in the machine chamber for cooling the magnetron and the high-voltage transformer simultaneously. During the operation of the magnetron, the cooling fan is operated to introduce outside air into the machine chamber and to direct the same toward the magnetron and the high-voltage transformer.
However, because of the restriction requirement for the height of the microwave oven, i.e. the height of the machine chamber, the cooling fan having an outer diameter larger than the height of the machine chamber cannot be located therein. Furthermore, since it is difficult to arrange the magnetron and the high-voltage transformer in closely adjacent relation, these are ordinarily arranged in a spaced apart relation in the machine chamber.
As a consequence, it has been found difficult to cool the high-voltage transformer and the magnetron in use of a single cooling fan, and accordingly, a microwave oven provided with a pair of cooling fans has been proposed to cool the two units separately.
However, in this type of conventional microwave oven, the height of the machine chamber cannot always be constant because of the construction errors and the like, and in order to prevent the cooling fans from contacting the walls of the machine chamber, the ratio of the outer diameter of each fan to the height of the machine chamber cannot be increased as desired. Thus, a comparatively small value had to be selected for the diameter ratio, so that a problem of unsatisfactory cooling of the electrical parts occurs.
Furthermore, because of the production errors of the parts of the microwave oven, it is difficult to equalize the gaps formed between the outer periphery of the cooling fan and the upper and lower walls of the machine chamber. Unequal gaps between the fan blades of each fan and the upper and lower walls of the machine chamber render the flow of air delivered from the cooling fan to be unstable and create vibrations and noises in the machine chamber. In order to equalize the gaps, a fine position adjusting device for the cooling fan is required and the assembling operation of the microwave oven is thereby complicated.
For economizing the construction cost, there has been proposed a microwave oven having a construction wherein the two cooling fans are driven by a single motor through a power transmission device such as an endless belt. However, when a trouble occurs in the belt to make one or both of the cooling fans inoperative, a hazardous condition tends to occur in the magnetron and/or the high-voltage transformer. Particularly, the temperature of the magnetron rises rapidly in comparison with the high-voltage transformer, so that it will be required to strictly watch or monitor the temperature rising of the magnetron.
Moreover, there remain several points to be improved for the conventional microwave oven such as improved ventilation or air exhausting condition in the machine chamber and the arrangement of the electric parts or components in the machine chamber for improving the air flowing effect therein.